Previous reports from unrandomized clinical trials have strongly suggested that the prophylactic transfusion of platelets in thrombocytopenic patients with acute leukemia significantly enhances their chance of remission and averts hemorrhagic complications. These data were based largely on observations in leukemic patients previously unexposed to platelet transfusions during their first course of induction therapy. Yet they have been translated into a requirement for continued prophylatic transfusion of thrombocytopenic leukemic patients even after they have become refractory to platelet transfusion. This practice constitutes a large usage of platelets in the United States even though its long range effects are not only untested and may be deleterious. The present study was designed to investigate the beneficial and potentially harmful effects of platelet transfusions in patients with acute myelogenous leukemia to determine if current practices should be altered. Presently, the major significant complications of platelet transfusions are exposure to hepatitis and the development of platelet antibodies. These problems and their effect upon the leukemic patient are the subjects of our investigations.